The present invention relates to cast molding of toric contact lenses, which include an optical zone providing a cylindrical correction for patients having certain astigmatic abnormalities. Unlike contact lenses having only a spherical correction, which may generally be placed on the eye in any rotational position, toric lenses are positioned on the patient""s eye such that the optical zone""s toric axis is aligned with the eye""s astigmatic axis.
To maintain a toric contact lens in position, it is well known to provide structure on the contact lens to orient the lens through the operation of gravity and/or eyelid movement. For example, the lens may be thinned and/or thickened, for example to provide ballast or slab-off, at various areas so that the eyelid""s movement during blinking moves the lens to the correct position. The particular design of this structure is not in and of itself critical to the present invention and is therefore not discussed in greater detail herein. For ease of discussion, all such structure, including slab-off, is generally referred to herein as xe2x80x9cballast.xe2x80x9d Because the ballast maintains the toric contact lens at a predetermined orientation on the eye, the toric optical zone is formed so that the toric axis is offset from the ballast orientation to align the toric axis with the patient""s astigmatic axis. This offset is often defined in increments, for example of 5xc2x0 or 10xc2x0.
Ballast is typically defined by the outer contact lens curve to prevent discomfort to the eye and to take advantage of eyelid movement. The toric optical zone may be defined on either the front or back lens curve. Depending on the method used to manufacture the lens, however, it may be desirable to define the toric surface on the back curve.
Where the lens is formed by a cast molding process, a monomer is typically deposited in a cavity between two mold halves that are themselves formed by injection molding. Each mold half defines an optical surface that forms either the front lens curve or the back lens curve. These optical surfaces are, in turn, formed by optical tools disposed in the mold cavity of an injection molding machine. Optical tools used to make toric lens molds therefore define the toric optical zone and ballast that are imparted to the mold halves. If the ballast and the toric optical zones are formed on the same lens surface, the optical tool forming that surface would define both characteristics. Thus, for given ballast and toric zone designs, a separate optical tool is required for every offset angle. To reduce the number of required optical tools, the ballast and the toric zone may therefore be defined on opposite contact lens surfaces, and therefore on opposite lens mold halves. For instance, the ballast may be defined by the front curve mold half while the toric optical zone is defined by the back curve mold half. Accordingly, the resulting mold halves may be rotated with respect to each other to achieve a desired offset angle.
Once the mold halves are formed, the lens-forming process using the mold may be automated to varying degrees. The present invention is directed to an improved apparatus for holding the mold halves during such a process and rotating the halves with respect to each other to achieve a desired rotational offset between them.
The present invention recognizes and addresses disadvantages of prior art constructions and methods.
Accordingly, it is an object of the present invention to provide an improved lens mold carrier.
This and other objects are achieved by a carrier according to the present invention for holding a lens mold. The lens mold includes a first mold half defining a first optical surface and a second mold half defining a second optical surface. The first mold half and the second mold half are configured to receive each other so that a lens forming cavity is defined between the first optical surface and the second optical surface. The carrier includes a first frame defining a front surface. A holder assembly is in operative communication with the first frame and is configured to receive the first mold half. The holder assembly is adjustable to rotationally secure the first mold half so that the first optical surface faces outward from the first frame front surface and in any of a plurality of rotational positions with respect to an axis normal to the first frame front surface. A second frame is configured to receive the second mold half so that the second optical surface faces outward from a front surface of the second frame. The second frame front surface opposes the first frame front surface upon alignment of the first frame and the second frame in an operative position.